Non-volatile random access memory (nvram) as a replacement for traditional mass storage

ABSTRACT

A non-volatile random access memory (NVRAM) is used in a computer system to perform multiple roles in a platform storage hierarchy, specifically, to replace traditional mass storage that is accessible by an I/O. The computer system includes a processor to execute software and a memory coupled to the processor. At least a portion of the memory comprises a non-volatile random access memory (NVRAM) that is byte-rewritable and byte-erasable by the processor. The system further comprises a memory controller coupled to the NVRAM to perform a memory access operation to access the NVRAM in response to a request from the software for access to a mass storage.

BACKGROUND

1. Field

Embodiments of the invention relate to a computer system; and morespecifically, to the use of non-volatile random access memory as areplacement for traditional mass storage.

2. Description of the Related Art

A. Current Memory and Storage Configurations

One of the limiting factors for computer innovation today is memory andstorage technology. In conventional computer systems, system memory istypically implemented by dynamic random access memory (DRAM). DRAM-basedmemory consumes power even when no memory reads or writes occur becauseit must constantly recharge internal capacitors. DRAM-based memory isvolatile, which means data stored in DRAM memory is lost once the poweris removed.

With respect to mass storage, conventional mass storage devicestypically include non-volatile magnetic media (e.g., hard disk drives)and/or flash memory (also referred to as “flash”) (e.g., solid statedrives (SSDs)). These storage devices are block-addressable, which meansthat a single byte of storage cannot be accessed individually. Rather,bytes are read and written as multi-byte (e.g., 16 bytes or larger)blocks of data. Generally, these storage devices are considered I/Odevices because they are accessed by the processor through various I/Oadapters that implement various I/O protocols. These I/O adapters andI/O protocols consume a significant amount of power and can have asignificant impact on the die area and the form factor of the platform.Additionally, for portable or mobile devices (e.g., tablet computers,cameras and mobile phones) that have limited battery life, their storagedevices (e.g., Embedded Multimedia Card (eMMC) and Secure Digital (SD)card) are typically coupled to the processor via low-power interconnectsand I/O controllers in order to meet active and idle power budgets.These interconnect and I/O controllers cannot consistently deliver thebandwidth required for a satisfying user experience.

With respect to firmware memory, a conventional computer systemtypically uses flash memory devices to store persistent systeminformation that is read often but seldom (or never) written to. Forexample, Basic Input and Output System (BIOS) images are typicallystored in a flash memory device. Flash memory devices that are currentlyavailable in the market generally have limited speed (e.g., 50 MHz).This speed is further reduced by the overhead for read protocols (e.g.,2.5 MHz). In order to speed up the BIOS execution speed, conventionalprocessors generally cache a portion of BIOS code during thePre-Extensible Firmware Interface (PEI) phase of the boot process.However, the processor cache has a very limited amount of capacity.Thus, the amount of BIOS code that can be used for the initial systemconfiguration is also very limited. The size limitation of the processorcache places a significant restriction on the size of the BIOS code usedin the PEI phase (also known as the “PEI BIOS code”). Therefore, the PEIBIOS code cannot be easily extended to support a large mix of memoryconfigurations and multiple processor families. With the rising demandfor initialization of processors, process interconnects, memory andstorage implemented with various technologies and multiple processorfamilies, the need for more versatile PEI BIOS code also grows. Onesolution is to build a larger processor cache for caching the code.However, the size of the processor cache cannot be easily increasedwithout a negative impact on the rest of the system.

B. Phase-Change Memory (PCM) and Related Technologies

Phase-change memory (PCM), also sometimes referred to as PCME, PRAM,PCRAM, Ovonic Unified Memory, Chalcogenide RAM and C-RAM, is a type ofnon-volatile computer memory which exploits the unique behavior ofchalcogenide glass. As a result of heat produced by the passage of anelectric current, this material can be switched between two states:crystalline and amorphous. Recent versions of PCM can achieve twoadditional distinct states, effectively doubling memory storagecapacity. PCM is one of a number of new memory technologies competing inthe non-volatile role with flash memory. Flash memory has a number ofpractical problems which these replacements hope to address.

For example, PCM can offer much higher performance in applications wherewriting quickly is important, in part because the memory element can beswitched more quickly, and also because individual bits may be changedto either 1 or 0 without the need to first erase an entire block ofcells (as is the case with flash). The high performance of PCM makes itpotentially very beneficial in non-volatile memory roles that arecurrently performance-limited by memory access timing.

Additionally, while PCM devices degrade with use (like flash), theydegrade much more slowly. A PCM device may survive approximately 100million write cycles. PCM lifetime is limited by mechanisms such asdegradation due to GST thermal expansion during programming, metal (andother material) migration, and other mechanisms.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. In the drawings:

FIG. 1 illustrates a computer system that uses non-volatile memoryrandom access (NVRAM) in one or more tiers of the platform storagehierarchy according to one embodiment of the invention.

FIG. 2 illustrates a computer system that uses NVRAM as a totalreplacement for traditional non-volatile mass storage and firmwarememory according to one embodiment of the invention.

FIG. 3 illustrates a decode logic that decodes an input addressaccording to one embodiment of the invention.

FIG. 4 illustrates a method of configuring the partitions within anNVRAM device according to one embodiment of the invention.

FIG. 5 illustrates an interface between software and storage provided bythe NVRAM of FIG. 2 according to a first embodiment of the invention.

FIG. 6A illustrates a memory and storage subsystem according to analternative embodiment of the invention.

FIG. 6B illustrates a memory and storage subsystem according to analternative embodiment of the invention.

FIG. 7 illustrates an interface between software and storage provided bythe NVRAM according to a second embodiment of the invention.

FIG. 8A illustrates an interface between software and storage providedby the NVRAM according to a third embodiment of the invention.

FIG. 8B illustrates the embodiment of FIG. 8A with further details.

FIG. 9 illustrates an interface between software and storage provided bythe NVRAM according to a fourth embodiment of the invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures and techniques have not been shown in detail inorder not to obscure the understanding of this description.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

In the following description and claims, the terms “coupled” and“connected,” along with their derivatives, may be used. It should beunderstood that these terms are not intended as synonyms for each other.“Coupled” is used to indicate that two or more elements, which may ormay not be in direct physical or electrical contact with each other,co-operate or interact with each other. “Connected” is used to indicatethe establishment of communication between two or more elements that arecoupled with each other.

Bracketed text and blocks with dashed borders (e.g., large dashes, smalldashes, dot-dash, dots) are sometimes used herein to illustrate optionaloperations/components that add additional features to embodiments of theinvention. However, such notation should not be taken to mean that theseare the only options or optional operations/components, and/or thatblocks with solid borders are not optional in certain embodiments of theinvention.

Embodiments of the invention described below define platformconfigurations that enable hierarchical memory subsystem organizationsfor the use of NVRAM. The use of NVRAM in the memory hierarchy alsoenables new usages such as expanded boot space and mass storageimplementations, as described in detail below.

FIG. 1 is a block diagram illustrating a computer system 100 that usesbyte-addressable non-volatile random-access memory (NVRAM) 130 in one ormore tiers of the platform storage hierarchy. The term “platform storagehierarchy” herein refers to the entire storage media used by computersystem 100 for storing data, instructions, states, and other persistentand non-persistent information. In one embodiment, all persistentstorage in the computer system 100 can coalesce into one NVRAM 130 in aconfigurable fashion. In addition, some portion of NVRAM 130 can beapportioned as DRAM replacement for system memory. The versatility ofNVRAM 130 facilitates technology migration from a conventional platformhaving an operating system (OS) that operates on a persistentblock-oriented file system, to an OS that understand a fully-persistent,byte-addressable, single-level data store.

In one embodiment, NVRAM 130 can be configured to implement the roles ina typical platform storage hierarchy as one or more of the following:cache, system memory (also known as main memory, primary memory,executable memory), storage (also known as secondary storage and massstorage), and firmware memory (such as boot memory (also known as BIOSflash), Trusted Platform Module (TPM) memory, Gigabit Ethernet networkintegrity controller (NIC) for storing its media access control (MAC)address, and the like). Platform storage hierarchies with differentroles are also contemplated and the application of NVRAM 130 is notlimited to the roles described above.

NVRAM (e.g., NVRAM 130) is distinguishable from other instruction anddata memory/storage technologies in terms of its characteristics and/orits application in the platform storage hierarchy. For example, NVRAM isdifferent from:

-   -   1) static random access memory (“SRAM”) applied as a cache        dedicated to a processor core or shared by multiple processor        cores;    -   2) higher speed memory (e.g., dynamic random access memory        (“DRAM”)) applied as one or more caches internal to the        processor (e.g., on the same die as the processor) and/or        external to processor (e.g., on the same or a different package        from the processor);    -   3) flash memory/magnetic disk/optical disc applied as drive        storage; and memory such as flash memory or read only memory        (ROM) applied as boot ROM.

In one embodiment of the invention NVRAM has the followingcharacteristics:

-   -   1) non-volatile (it maintains its content even if power is        removed, similar to flash memory used in solid state disks        (“SSD”), and different from SRAM and DRAM which are volatile);    -   2) lower power consumption than volatile memories such as SRAM        and DRAM;    -   3) random access (also known as randomly addressable);    -   4) rewritable and erasable at a lower level of granularity        (e.g., byte level) than flash found in SSDs (which can only be        rewritten and erased a “block” at a time—minimally 64 Kbyte in        size for NOR flash and 16 Kbyte for NAND flash);    -   5) usable as a system memory and allocated all or a portion of        the system address space; and    -   (6) capable of being coupled to the processor over a bus using a        transactional protocol (a protocol that supports transaction        identifiers (IDs) to distinguish different transactions so that        those transactions can complete out-of-order) and allowing        access at a level of granularity small enough to support        operation of the NVRAM as system memory (e.g., cache line size        such as 64 or 128 byte). For example, the bus may be a memory        bus (e.g., a DDR bus such as DDR3, DDR4, etc.) over which is run        a transactional protocol as opposed to the non-transactional        protocol that is normally used. As another example, the bus may        one over which is normally run a transactional protocol (a        native transactional protocol), such as a PCI express (PCIE)        bus, desktop management interface (DMI) bus, or any other type        of bus utilizing a transactional protocol and a small enough        transaction payload size (e.g., cache line size such as 64 or        128 byte);    -   7) one or more of the following:        -   a) faster write speed than current non-volatile            memory/storage technologies (such as flash);        -   b) very high read speeds (faster than flash and near or            equivalent to DRAM read speeds);        -   c) directly writable (rather than requiring erasing            (overwriting with 1s) before writing data like flash memory            used in SSDs); and/or        -   d) orders of magnitude (e.g., 2 or 3) higher write endurance            before failure (more than boot ROM and flash used in SSDs).

As mentioned above, in contrast to flash memory, which must be rewrittenand erased a complete “block” at a time, the level of granularity atwhich NVRAM is accessed in any given implementation may depend on theparticular memory controller and the particular memory bus to which theNVRAM is coupled. For example, in some implementations where NVRAM 130is used as system memory, NVRAM may be accessed at the granularity of acache line (e.g., a 64-byte or 128-byte cache line), notwithstanding aninherent ability to be accessed at the granularity of a byte, becausecache line is the level at which the memory subsystem accesses memory.Thus, when NVRAM is deployed within a memory subsystem, it may beaccessed at the same level of granularity as the DRAM (e.g., the “nearmemory”) used in the same memory subsystem. Even so, the level ofgranularity of access to the NVRAM by the memory controller and memorybus or other type of bus is smaller than that of the block size used byflash and the access size of the I/O subsystem's controller and bus.

NVRAM 130 may be used as instruction and data storage that hassufficiently short access time requirements to cause little impact onthe processors. Here, program instructions and data may be loaded intoNVRAM 130 from deeper, flash/magnetic/optical mass storage 152 prior tobeing executed by the processors. Moreover, as described in detailbelow, NVRAM 130 may be placed on a memory bus and may communicatedirectly with a memory controller that, in turn, communicates directlywith the processors.

The presence of the new memory technology for NVRAM 130 provides for awealth of new possibilities. Although discussed at much greater lengthfurther below, some of these possibilities are quickly highlightedimmediately below.

According to one possible implementation, NVRAM 130 acts as a totalreplacement or supplement for traditional DRAM technology in systemmemory. In one embodiment, NVRAM 130 represents the introduction of asecond-level system memory (e.g., system memory is as a combination ofDRAM 140 and some or all of NVRAM 130). As such, the system memory maybe viewed as having a near memory part NM 141A and a far memory part FM142. It is appreciated that in different embodiments, a near memory canserve as a memory-side cache (e.g., near memory cache 141B), a scratchpad, and other roles that are different from the system memory. In theembodiments described herein, the NM 141A portion of NVRAM 130 servesonly as system memory to simplify the discussion.

According to some embodiments, NVRAM 130 provides NVRAM storage, whichacts as a total replacement or supplement for traditional mass storage,e.g., flash/magnetic/optical mass storage 152. The term “traditionalmass storage” or in the application refers to mass storage that is basedon optical, magnetic and/or flash technology, such as disk and flashmemory. For simplicity of the discussion, flash/magnetic/optical massstorage 152 is also referred to as traditional mass storage 152. Thus,the non-volatile mass storage for computing system 100 may beimplemented using NVRAM, flash memory, magnetic storage, or anycombination thereof. In an embodiment where NVRAM storage 150 acts as atotal replacement for traditional mass storage 152, it is not necessaryto use storage drivers for block-addressable storage access. The removalof storage driver overhead from storage access can increase access speedand save power. In alternative embodiments where it is desired thatNVRAM storage 150 appears to the OS and/or applications asblock-accessible and indistinguishable from traditional mass storage152, emulated storage drivers can be used to expose block-accessibleinterfaces (e.g., Universal Serial Bus (USB) Bulk-Only Transfer (BOT)1.0, Serial Advanced Technology Attachment (SATA) 3.0, and the like) tothe software for accessing NVRAM storage 150. In some embodiments, thebyte addressability of NVRAM 130 can be used by a lowest-level storagedriver to move blocks of NVRAM storage 150 and emulate block accessiblemass storage without incurring the cost of I/O interfaces. An embodimentof utilizing the byte addressability of NVRAM 130 with a lowest-levelstorage driver will be described later in greater detail with referenceto FIG. 5.

According to some embodiments, NVRAM 130 provides BIOS NVRAM 160 and TPMNVRAM 170, which act as a total replacement or supplement for firmwarememory such as BIOS flash 162 and TPM flash 172. Firmware memory iscommonly implemented with flash technology and commonly stores theinitial instructions (e.g., BIOS) executed by a processor to initializekey system components during a boot process. Firmware memory can alsostore system persistent states used by a TPM 134 to protect sensitivesystem information (e.g., encryption keys). In one embodiment, the useof NVRAM 130 for firmware memory removes the need for third party flashparts to store code and data that are critical to the system operations.

The choice of memory and storage devices may depend on the type ofplatform on which the devices are used. For example, in a personalcomputer, tablet computer, notebook computer, mobile device (e.g.,smartphone or PDA), the non-volatile mass storage may be implementedusing NVRAM storage 150 alone, or using NVRAM storage 150 in combinationwith flash/magnetic storage. In other implementations (e.g., large-scaleservers), the non-volatile mass storage may be implemented usingmagnetic storage (e.g., hard drives) or any combination of magneticstorage, flash, and NVRAM storage 150. In such a case, computer systemhardware and/or software responsible for storage may implement variousintelligent persistent storage allocation techniques to allocate blocksof persistent program code and data between the FM 142/NVRAM storage 150and traditional mass storage 152 in an efficient or otherwise usefulmanner. In some embodiments, NVRAM 130 may become the solememory/storage device off chip (i.e., off the processor chip). In someembodiments, instead of the off-chip DRAM 140, DRAM may be used toprovide an on-chip cache (e.g., near memory cache 141B). Theseembodiments can be specifically relevant to very small platforms (e.g.,smartphone or PDA), where multiple memory classes/technologies may becost prohibitive and more transistors (including storage) can be placedon chip.

The NVRAM 130 may incorporate “wear leveling” algorithms to account forthe fact that the storage cells at the far memory level begin to wearout after too many write accesses. Since high cycle count blocks aremost likely to wear out in this manner, wear leveling spreads writesacross the far memory cells by swapping addresses of high cycle countblocks with low cycle count blocks. Note that most address swapping istypically transparent to the end user because it is handled by hardware,software (e.g., a low level driver or operating system), or acombination of the.

In one embodiment, NVRAM 130 can be implemented with a non-volatilerandom access memory (NVRAM) such as PCM or, more specifically, PCMS(also known as (PRAM or PCRAM), Ovonic Unified Memory (OUM), (CRAM).Other possible technology choices for far memory include, but are notlimited to byte-addressable persistent memory (BPRAM), storage classmemory (SCM), universal memory, Ge2Sb2Te5, Programmable metallizationcell (PMC), Resistive memory (RRAM), RESET (amorphous) cell, SET(crystalline) cell, PCME, Ovshinsky, ferroelectric memory (also known aspolymer memory and poly(N-vinylcarbazole)), ferromagnetic memory (alsoknown as Spintronics, SPRAM (spin-transfer torque RAM), STRAM (spintunneling RAM), Magnetoresistive, Magnetic memory, and Magnetic randomaccess memory (MRAM)), andSemiconductor-oxide-nitride-oxide-semiconductor (SONOS, also knowdielectric memory).

For convenience of explanation, most of the remainder of the applicationwill sometimes refer to “PCM” or “PCMS” as the technology selection forNVRAM 130. As such, the terms NVRAM, PCM and PCMS may be usedinterchangeably in the following discussion. However it should berealized, as discussed above, that different technologies may also beutilized for NVRAM 130.

Continuing then with a discussion of the system of FIG. 1, in someembodiments, the architecture of computer system 100 may includemultiple processors, although a single processor 110 is illustrated inFIG. 1 for simplicity. Processor 110 may be any type of data processorincluding a general purpose or special purpose central processing unit(CPU), an application-specific integrated circuit (ASIC) or a digitalsignal processor (DSP). For example, processor 110 may be ageneral-purpose processor, such as a Core™ i3, i5, i7, 2 Duo and Quad,Xeon™, or Itanium™ processor, all of which are available from IntelCorporation, of Santa Clara, Calif. Alternatively, processor 110 may befrom another company, such as ARM Holdings, Ltd, of Sunnyvale, Calif.,MIPS Technologies of Sunnyvale, Calif., etc. Processor 110 may be aspecial-purpose processor, such as, for example, a network orcommunication processor, compression engine, graphics processor,co-processor, embedded processor, or the like. Processor 110 may beimplemented on one or more chips included within one or more packages.Processor 110 may be a part of and/or may be implemented on one or moresubstrates using any of a number of process technologies, such as, forexample, BiCMOS, CMOS, or NMOS.

In one embodiment, the processor 110 includes an integrated graphicsunit 111 which includes logic for executing graphics commands such as 3Dor 2D graphics commands. While the embodiments of the invention are notlimited to any particular integrated graphics unit 111, in oneembodiment, the graphics unit 111 is capable of executing industrystandard graphics commands such as those specified by the Open GL and/orDirect X application programming interfaces (APIs) (e.g., OpenGL 4.1 andDirect X 11).

The processor 110 may also include one or more cores 112, although asingle core 112 is illustrated in FIG. 1, again, for the sake ofclarity. In many embodiments, core 112 includes internal functionalblocks such as one or more execution units, retirement units, a set ofgeneral purpose and specific registers, etc. If core 112 ismulti-threaded or hyper-threaded, then each hardware thread may beconsidered as a “logical” core as well. The cores 112 may be homogenousor heterogeneous in terms of architecture and/or instruction set. Forexample, some of the cores may be in order while others areout-of-order. As another example, two or more of the cores may becapable of executing the same instruction set, while others may becapable of executing only a subset of that instruction set or adifferent instruction set.

The processor 110 may also include one or more caches, such as cache 113which may be implemented as a SRAM and/or a DRAM. In many embodimentsthat are not shown, additional caches other than cache 113 areimplemented so that multiple levels of cache exist between the executionunits in the core(s) 112 and memory devices 141A and 142. For example,the set of shared cache units may include an upper-level cache, such asa level 1 (L1) cache, mid-level caches, such as level 2 (L2), level 3(L3), level 4 (L4), or other levels of cache, a last level cache (LLC),and/or different combinations thereof. In different embodiments, cache113 may be apportioned in different ways and may be one of manydifferent sizes in different embodiments. For example, cache 113 may bean 8 megabyte (MB) cache, a 16 MB cache, etc. Additionally, in differentembodiments the cache may be a direct mapped cache, a fully associativecache, a multi-way set-associative cache, or a cache with another typeof mapping. In other embodiments that include multiple cores, cache 113may include one large portion shared among all cores or may be dividedinto several separately functional slices (e.g., one slice for eachcore). Cache 113 may also include one portion shared among all cores andseveral other portions that are separate functional slices per core. Inone embodiment, cache 113 may include a DRAM near memory cache 141B.

The processor 110 may also include a home agent 114 which includes thosecomponents coordinating and operating core(s) 112. The home agent unit114 may include, for example, a power control unit (PCU) and a displayunit. The PCU may be or include logic and components needed forregulating the power state of the core(s) 112 and the integratedgraphics unit 111. The display unit is for driving one or moreexternally connected displays.

In some embodiments, processor 110 includes an integrated memorycontroller (IMC) 131 to provide an interface for communicating with amemory and storage subsystem 180. More specifically, in one embodiment,IMC 131 contains logic necessary for reading from, writing to andrefreshing DRAM device 140. IMC 131 can be on the same chip as processor110, or on a separate chip and/or package connected to processor 110.

In some embodiments, processor 110 includes an I/O subsystem 115 coupledto IMC 131. I/O subsystem 115 enables communication between processor110 and the following serial or parallel I/O devices: one or morenetworks 136 (such as a Local Area Network, Wide Area Network or theInternet), storage I/O device (such as traditional mass storage 152,BIOS flash 162, TPM flash 172) and one or more non-storage I/O devices137 (such as display, keyboard, speaker, and the like). I/O subsystem115 may include a platform controller hub (PCH) (not shown) that furtherincludes several I/O adapters 138 and other I/O circuitry to provideaccess to the storage and non-storage I/O devices and networks. Toaccomplish this, I/O subsystem 115 may have at least one integrated I/Oadapter 138 for each I/O protocol utilized. I/O subsystem 115 can be onthe same chip as processor 110, or on a separate chip and/or packageconnected to processor 110.

I/O adapters 138 translate a host communication protocol utilized withinthe processor 110 to a protocol compatible with particular I/O devices.For traditional mass storage 152, some of the protocols that I/Oadapters 138 may translate include Peripheral Component Interconnect(PCI)-Express 3.0, Universal Serial Bus (USB) 3.0, Serial AdvancedTechnology Attachment (SATA) 3.0, Small Computer System Interface(SCSI), Redundant Array of Inexpensive Disks (RAID) and 1394 “Firewire,”among others. For BIOS flash 162, some of the protocols that I/Oadapters 138 may translate include Serial Peripheral Interface (SPI),Microwire, among others. Additionally, there may be one or more wirelessprotocol I/O adapters. Examples of wireless protocols are Bluetooth 4.0,IEEE 802.11-based wireless protocols, and cellular protocols, amongothers.

In some embodiments, I/O subsystem 115 also includes a Management Engine(ME) 135, which is a microprocessor that allows a system administratorto monitor, maintain, update, upgrade, and repair computer system 100.In one embodiment, a system administrator can remotely configurecomputer system 100 through ME 135 via networks 136. In one embodiment,the configuration can be stored in a decode table 133 within processor110. Decode table 133 can be read by IMC 131 and I/O subsystem 115,which then decide where a data access request should be directed.

In some embodiments, processor 110 includes a Trusted Platform Module(TPM) 134 to control access to system persistent states, such as securedata, encryption keys, platform configuration information and the like.In one embodiment, these system persistent states are stored in a TPMNVRAM 170, which can be implemented with PCM-based memory such as PCMS.In the embodiment shown in FIG. 1, TPM NVRAM 170 is part of NVRAM 130.

In one embodiment, TPM 134 is a secure micro-controller withcryptographic functionalities. TPM 134 has a number of trust-relatedcapabilities; e.g., a “seal” capability for ensuring that data protectedby a TPM is only available for the same TPM. TPM 134 can protect dataand keys (e.g., secrets) using its encryption capabilities. In oneembodiment, TPM 134 has a unique and secret RSA key (which is generatedbased on the RSA algorithm developed by Ron Rivest, Adi Shamir andLeonard Adleman), which allows it to authenticate hardware devices andplatforms. For example, TPM 134 can verify that a system seeking accessto data stored in computer system 100 is the expected system. TPM 134 isalso capable of reporting the integrity of the platform (e.g., computersystem 100). This allows an external resource (e.g., a server on anetwork) to determine the trustworthiness of the platform but does notprevent access to the platform by the user.

It should be understood that a computer system can utilize NVRAM 130 forsystem memory, mass storage, firmware memory and/or other memory andstorage purposes even though its processor does not have all of theabove-described components of processor 110, or has more components thanprocessor 110.

In one embodiment, computer system 100 includes a NVRAM controller 132to control data access to NVRAM 130. NVRAM controller 132 is coupled toIMC 131 and I/O subsystem 115. NVRAM controller 132 can read theconfiguration data from decode table 133, or alternatively, can rely onthe decoding results passed from IMC 131 and I/O subsystem 115. In anembodiment where NVRAM 130 is implemented with PCMS, NVRAM controller132 is a PCMS controller that performs byte-level access with protocolsconsistent with the PCMS technology. Although IMC 131 and NVRAMcontroller 132 can be two discrete controllers (as shown in FIG. 1 witha dotted line separating the two controllers), in some embodiments thesetwo controllers can be implemented as one combined controller to controlthe access to memory and storage.

In FIG. 1, NVRAM controller 132 is shown connected to FM 142, NVRAM massstorage 150 and BIOS NVRAM 160 using three separate lines. This does notnecessarily mean, however, that there are three separate physical busesor communication channels connecting NVRAM controller 132 to theseportions of the NVRAM 130. Rather, in some embodiments, a common memorybus or other type of bus is used to communicatively couple the NVRAMcontroller 132 to the FM 142, NVRAM mass storage 150, and BIOS NVRAM160. For example, in one embodiment, the three lines in FIG. 1 representa DDR bus, such as a memory bus (e.g., a DDR3, DDR4, etc.) over whichNVRAM controller 132 implements a transactional protocol to communicatewith NVRAM 130. NVRAM controller 132 may also communicate with NVRAM 130over a bus supporting a native transactional protocol such as a PCIexpress (PCI-E) bus, desktop management interface (DMI) bus, or anyother type of bus utilizing a transactional protocol.

FIG. 2 is a block diagram illustrating a computer system 200 that usesNVRAM 130 as a total replacement for traditional mass storage 152 andfirmware memory (e.g., BIOS flash 162 and TPM flash 172) according toone embodiment of the invention. Computer system 200 includes aprocessor 210 coupled to a memory and storage subsystem 280. In thisembodiment, memory and storage subsystem 280 includes DRAM device 140and NVRAM 130 only. As described above, NVRAM 130 has configurablepartitions including system memory (FM 142), mass storage (NVRAM storage150) and firmware memory (BIOS NVRAM 160 and TPM NVRAM 170). Processor210 can be the same as processor 110 of FIG. 1, except that I/O adaptors238 do not necessarily include all of adaptors 138 of FIG. 1 foraccessing traditional mass storage and flash memory. In such a case,computer system hardware and/or software responsible for memory andstorage access may implement various intelligent techniques to benefitfrom the low-latency, high-throughput and robustness of NVRAM 130 (ascompared to the traditional flash/magnetic storage, such as traditionalmass storage 152, BIOS NVRAM 162 and TPM NVRAM 172).

Configurable Partitioning of the NVRAM

As described before, NVRAM 130 can be partitioned into multiplepartitions that have different roles in a platform storage hierarchy. Asdiscussed above, the term “platform storage hierarchy” refers to cache,system memory, mass storage, and firmware memory that serve differentpurposes (e.g., BIOS storage and TPM storage). In one embodiment, themeans by which access is steered to different partitions of NVRAM 130 isvia a decode logic. For example, at either manufacturing time or in thefield, computer system 100 can program decode table 133 to markdifferent regions of NVRAM 130 as system memory, mass storage, firmware,among others.

In the embodiment of FIGS. 1 and 2, NVRAM 130 is partitioned into FM142, NVRAM storage 150, BIOS NVRAM 160 and TPM NVRAM 170. The addressrange of each partition can be defined in decode table 133. In oneembodiment, when IMC 131 receives an access request, the target addressof the request is decoded to reveal whether the request is directedtoward memory or I/O. If it is a memory request, IMC 131 furtherdetermines from the target address whether the request is directed to NM141A or FM 142. For FM 142 access, IMC 131 forwards the request to NVRAMcontroller 132. IMC 131 passes the request to the I/O subsystem 115 ifthis request is directed to I/O (e.g., non-storage and storage I/Odevices). I/O subsystem 115 further decodes the address to determinewhether the address points to NVRAM storage 150, BIOS NVRAM 162, orother non-storage and storage I/O devices. If this address points toNVRAM storage 150 or BIOS NVRAM 162, I/O subsystem 115 forwards therequest to NVRAM controller 132. If this address points to TPM NVRAM170, I/O subsystem 115 passes the request to TPM 134 to perform securedaccess. In one embodiment, each request forwarded to NVRAM controller132 is accompanied with an attribute (also known as a “transactiontype”) to indicate the type of access. In one embodiment, NVRAMcontroller 132 may emulate the access protocol for the requested accesstype, such that the rest of the platform remains unaware of the multipleroles performed by NVRAM 130 in the platform storage hierarchy. Inalternative embodiments, NVRAM controller 132 may perform memory accessto NVRAM 130 regardless of which transaction type it is. It isunderstood that the decode path can be different from what is describedabove. For example, IMC 131 may decode the target address of an accessrequest and determine whether it is directed to NVRAM 130. If it isdirected to NVRAM 130, IMC 131 generates an attribute according todecode table 133. Based on the attribute, IMC 131 then forwards therequest to appropriate downstream logic (e.g., NVRAM controller 132 andI/O subsystem 115) to perform the requested data access. In yet anotherembodiment, NVRAM controller 132 may decode the target address if thecorresponding attribute is not passed on from the upstream logic (e.g.,IMC 131 and I/O subsystem 115). Other decode paths may be implemented.

FIG. 3 illustrates a decode logic 330 that decodes an input address andgenerates an output indicating one of the NVRAM partitions according toone embodiment of the invention. In one embodiment, the input address isa physical address pointing to a location (e.g., a byte location) withinNVRAM 130. In one embodiment, the physical address can be translatedfrom a system address (e.g., the address generated by cores 113) by atranslation logic 320. The output of decode logic 330 indicates thepartition of NVRAM 130 to which the input address is directed. In oneembodiment, the output indicates a NVRAM partition by its correspondingattributes; for example, 00 for FM 142, 01 for NVRAM storage 150, forBIOS NVRAM 160 and 11 for TPM NVRAM 170. It is understood that theattributes can be represented by any digital or analog indicators andare not limited by the example described and shown herein. Further,decode logic 330 can map input addresses to more or fewer partitionsthan the embodiment shown in FIG. 3. For example, if NVRAM 130 isconfigured (according to decode table 133) to contain only twopartitions, decode logic 330 can map input addresses to the twopartitions.

In one embodiment, decode logic 330 decodes input addresses based on theconfiguration data stored in decode table 133. In one embodiment, decodetable 133 stores an attribute 311, a base address 312 and a length 313for each of the partitions in NVRAM 130. Decode table 133 can be builtby the BIOS at boot time. For example, the BIOS can read theconfiguration data stored in control status registers (CSRs) 310 at boottime. CSRs 310 may include a range (e.g., a size) for each partition tobe configured in NVRAM 130. The BIOS then builds decode table 133accordingly.

It should be noted that decode logic 330 is a logical representation ofthe decoding operations performed within the platform (e.g., computersystem 100 of FIG. 1 or computer system 200 of FIG. 2). The hardwarethat implements decode logic 330 may reside in a single function unit(e.g., IMC 131) or in multiple function units (e.g., any combination ofIMC 131, I/O subsystem 115 and/or NVRAM controller 132). Similarly,translation logic 320 may be implemented by a single function unit(e.g., IMC 131), by multiple function units (e.g., any combination ofIMC 131, I/O subsystem 115 and/or NVRAM controller 132), or by acombination of software and hardware. Decode logic 330 and/ortranslation logic 320 may also reside outside of and coupled to IMC 131,I/O subsystem 115 and NVRAM controller 132. For simplicity ofillustration, the embodiments of FIGS. 1 and 2 show that each of IMC131, I/O subsystem 115 and NVRAM controller 132 has a connection todecode table 133 to indicate the possibility that all of them may readfrom decode table 133 to perform the function of decode logic 330.However, it should be understood that in alternative embodiments, onlyIMC 131 is, or IMC 131 and I/O subsystem 115 are, connected to decodetable 133 to perform the function of decode logic 330.

In one embodiment, CSRs 310 can be implemented by hardware fuses (e.g.,programmable read-only memory (PROM) that is programmable only once),re-programmable ROM (e.g., electrically-erasable programmable ROM(EEPROM)), or other programmable hardware. In an embodiment where decodetable 133 is re-programmable, those address ranges in decode table 133can be remotely programmed by an authorized server as described in theembodiment of FIG. 4.

FIG. 4 is a flow diagram illustrating a method 400 of configuring thepartitions within an NVRAM according to one embodiment of the invention.For simplicity of discussion, the operations of the flow diagram of FIG.4 will be described with reference to the embodiment of FIG. 1. However,it should be understood that the operations of the flow diagram can beperformed by the embodiment of FIG. 2, as well as embodiments other thanthose shown in these figures. Additionally, the embodiments discussedwith reference to FIGS. 1 and 2 can perform operations different thanthose discussed with reference to the flow diagram of FIG. 4.

Referring to FIGS. 1 and 4, in one embodiment, computer system 100requests configuration data from an authorized server for configuringthe partitions with NVRAM 130 via a network connection (block 410). Theauthorized server may be controlled or owned by a manufacturer ofcomputer system 100, a third-party authority, or any authority thatholds the rights to configure the NVRAM 130. Via the network connection,computer system 100 (e.g., ME 135) can send its credentials (e.g.,encryption keys, which are securely stored in TMP NVRAM 170) to theauthorized server (block 420). After the authorized server authenticatescomputer system 100, it sends back a signed message including therequested configuration data (block 430). Upon receiving the signedmessage, MC 135 can set CSRs 310 according to the received addressranges (block 440), such that decode table 133 can be programmed at boottime. Computer system 100 then reboots (block 450). During boot time,the BIOS of computer system 100 programs decode table 133 (block 460).The BIOS also propagates the configuration to the OS; e.g., the BIOS canbuild a number of tables that contains the configuration data for OS toread (block 470).

After computer system 100 is fully booted up and upon receipt of a dataaccess request with an NVRAM physical address, decode logic 330 decodesthe address indicated in the request based on the configuration data indecode table 133 (block 480). Decode logic 330 generates an attributeindicating one of the partitions in NVRAM 130 (block 490). Based on theattribute, decode logic 330 forwards the request to appropriatedownstream logic (e.g., I/O adaptors 138, TPM 134, and the like) (block495). The request may be forwarded with a transaction type indicating anattribute of the NVRAM partition. In one embodiment, the downstreamlogic can determine the appropriate protocol for accessing the partitionbased on the attribute.

In one embodiment, one of these tables created at block 470 is anaffinity table, which stores a logical distance for each underlyingmemory device. The affinity table allows kernel-level OS code todifferentiate between different portions of the system memory that areimplemented with different technologies, such as DRAM (NM 141A) andNVRAM (FM 142), and to appropriate OS page migration policy accordingly.For example, NM 141A can be used for frequently accessed data to absorbsome of the writes during regular operation of the computer system 100.

In one embodiment, the affinity table includes a logical distance for arange of memory addresses, where the logical distance indicates anactual physical distance, a domain, an access speed/time, or any othermetric to represent an access time or distance of a local memory. Basedon the information in the affinity table, the OS can direct memoryaccesses to different locations of memories. For example, an OS can makethread scheduling decisions and resource allocation to operations basedon the logical distance of a local memory. Numerous considerations, suchas the time critical nature of the operation, may be used to determinewhich local memory to utilize. For example, an operation that isextremely time-critical can be scheduled to utilize a DRAM (NM 141A), asit is represented in the affinity table by a shorter logical distancethan FM 141A. In the alternative, a thread that is to run in thebackground, which is not time intensive, can be scheduled to use FM141A, to ensure that NM 142 is available for other operations. Otherconsiderations such as the size of local memory, the type of thread oroperation to be executed or performed, or any other known considerationfor choosing a memory based on access distance or speed that may be usedin determining which local memory to utilize.

Removing Storage Driver Overhead in Storage Access

As described above, NVRAM 130 is non-volatile and randomly accessible.It can be accessed at the granularity of a byte and its access latencyis close to today's volatile RAM. As this non-volatile memory offershigh capacities closer to traditional storage media, it can replacetraditional I/O attached non-volatile mass storage devices in theplatform.

As shown in FIG. 2, the use of NVRAM 130 for both system memory (e.g.,FM 142) and NVRAM storage 150 can blur the line between the roles ofthese two different tiers in the platform storage hierarchy. Since bothFM 142 and NVRAM storage 150 reside in the same NVRAM 130, they can beviewed as one continuous partition and can be accessed in the same wayvia the same memory interconnects. Thus, the use of NVRAM storage 150can remove the burden of traditional I/O data access. That is, I/Oprotocols such as SATA, PCI-E, and the like, are no longer necessary forstorage access. As a result, in some embodiments, NVRAM storage 150 canbe accessed without a storage driver performing I/O operations, andinstead using CPU memory instructions to copy from storage to memorybuffers, thus emulating block access for the OS and applicationsoftware. Alternately, the OS file system can be aware of the memoryaddressable storage (i.e., NVRAM storage 150), and directly map theNVRAM storage 150 address space into the application address space. Thissaves the cost of the copying and the amount of memory used in thesystem. NVRAM storage 150 is herein referred to as “memory addressable,”because it is directly addressable in the physical memory address spaceand all of the instructions that use memory addresses as oprands willwork with the addresses of NVRAM storage 150.

However, legacy software (e.g., OS and applications) may still operateon the assumption that a storage driver exists in the computer system toperform block access. For example, typical legacy operating systemsconsider data that is in the mass storage but not in the system memoryas non-resident, and would trigger a page fault when that data isaccessed. A page fault handler then signals the storage driver to bringthe data into the system memory. This can be handled in the storagedriver by emulating block storage. Alternately, in an OS with a filesystem aware of the memory addressable storage, page fault handling maybe memory-map operation instead of a memory copy or I/O operations.

The benefits of removing the I/O interface and I/O controllers, as wellas the reduction of access cost, generally outweigh the cost of softwaremodification due to power saving and increase of speed in storageaccess. Embodiments of the invention use the PCMS as high-performancestorage in the platform, taking advantage of its properties of lowpower, high capacity, non-volatility and memory mode. Embodiments of theinvention remove the traditional storage stack I/O path and make thestorage addressable and cacheable by a processor to achieve fastestperformance at lowest power.

Embodiments of the invention provide an interface between software andstorage (implemented by NVRAM such as PCMS) at a number of levels, whichwill be described below with reference to FIGS. 5, 7, 8A, 8B and 9.Software (e.g., the OS and applications) and hardware operations shownin these figures can be executed by the embodiment of processor 110 and210 of FIGS. 1 and 2, as well as embodiments other than those shown inthese figures. Additionally, the embodiments discussed with reference toFIGS. 1 and 2 can perform different operations than those discussed withreference to the diagram of FIGS. 5, 7, 8A, 8B and 9.

FIG. 5 illustrates an interface between software and storage provided byNVRAM 130 of FIG. 2 according to a first embodiment of the invention. Inthis embodiment, IMC 131 has the additional capability of abstractingNVRAM 130 as traditional non-volatile mass storage (e.g., disks or flashmemory) for the software. IMC 131 is coupled to a storage driver 513,which can be implemented in software. To storage driver 513, IMC 131serves as traditional non-volatile mass storage that isblock-addressable. Computer system 200 uses this storage driver 513 asthe lowest-level disk driver. In this embodiment, software (OS 512 andapplications) can utilize data in NVRAM 130 without modification to thesoftware. That is, data access to a non-resident page (a page not in thesystem memory) will trigger a page fault and a disk I/O will beperformed.

In the embodiment shown in FIG. 5, when OS 512 initiates a storage I/O(e.g., in response to a page fault to bring in a page that is notresident in the system memory such as NM 141A and FM 142), it callsstorage driver 513 and provides a memory address, a storage address, alength and an operation type (e.g., read or write) (block 510). Storagedriver 513 communicates these parameters to IMC 131 using an interfacedifferent from standard I/O interfaces/protocols such as SATA 3.0, PCI-E3.0, and the like (block 520). The memory address indicates a memorylocation (in either NM 141A or FM 142) that is to swap pages with thestorage location specified by the storage address. IMC 131 translatesthe storage address into a physical address in NVRAM 130 (block 530).NVRAM controller 132 (or IMC 131 if it implements the protocol foraccessing NVRAM 130) then copies data from the memory address to thestorage address (if the operation is read), or copies data from thestorage address to the memory address (if the operation is write) (block540).

In one embodiment, the memory address falls within the address space ofFM 142. In this embodiment, IMC 131 also translates the memory addressinto a physical address in NVRAM 130. NVRAM controller 132 (or IMC 131if IMC can directly access NVRAM 130) then copies data between thememory address and the storage address by performing a memory-to-memorycopy within the same NVRAM. In another embodiment where the memoryaddress falls within the address space of NM 141A, the copy involves amemory-to-memory copy between two memory devices (e.g., NVRAM 130 andDRAM 140). After the copy is completed, IMC 131 signals storage driver513 (block 550), which in turn signals OS 512 indicating that the I/O iscompleted.

FIG. 6A illustrates a memory and storage subsystem 680 according to analternative embodiment of the invention. In this embodiment, memory andstorage subsystem 680 replaces NVRAM storage 150 (FIG. 2) with a RAMdisk 650 created by an OS. RAM disk 650 serves as storage for a filesystem 660. The use of RAM disk 650 as storage is described in furtherdetail with respect to the flow diagram of FIG. 7. NVRAM 130 may includemore or fewer partitions than what is shown in FIG. 6A (e.g., BIOS NVRAM162 and/or TPM NVRAM 172 may be absent). In one embodiment, RAM disk 650is configured and formatted during OS installation, and persists acrosssystem boots (like a regular disk).

FIG. 7 illustrates an interface between software and storage provided byNVRAM 130 according to a second embodiment of the invention. This secondembodiment refers to memory and storage subsystem 680 of FIG. 6A, inwhich the “storage” is a partition within FM 142 designated by an OS 712as RAM disk 650 (also known as “RAMDisk”). OS 712 treats RAM disk 650 asa traditional non-volatile mass storage device (e.g., disks orsolid-state drives). Access to RAM disk 650 is controlled by akernel-level driver, referred to as RAM disk driver 713, which presentsa standard disk drive to OS 712 and serves as the lowest-level diskdriver. In this embodiment, software (OS 712 and applications) canutilize data in NVRAM 130 without modification to the software. That is,data access to a non-resident page (a page not in the system memory)will trigger a page fault and a disk I/O will be performed.

In the embodiment shown in FIG. 7, when OS 712 initiates a disk I/O(e.g., in response to a page fault to bring in a page that is notresident in the system memory such as NM 141A and FM 142 of FIG. 6A), itcalls the RAM disk driver 713 and provides a memory address, a storageaddress, a length and an operation type (e.g., read or write) (block710). The memory address indicates a memory location (in either NM 141Aor FM 142) that is to swap pages with the storage location specified bythe storage address. IMC 131 translates the storage address into aphysical address in NVRAM 130 (block 720). NVRAM controller 132 (or IMC131 if it implements the protocol for accessing NVRAM 130) then copiesdata from the memory address to the storage address (if the operation isread), or copies data from the storage address to the memory address (ifthe operation is write) (block 730).

In one embodiment, the memory address falls within the address space ofFM 142. In this embodiment, RAM disk driver 713 also translates thememory address into a physical address in NVRAM 130. NVRAM controller132 (or IMC 131 if IMC can directly access NVRAM 130) then copies databetween the memory address and the storage address by performing amemory-to-memory copy within the same NVRAM device. In anotherembodiment where the memory address falls within the address space of NM141A (which acts as system memory), the copy involves a memory-to-memorycopy between two memory devices (e.g., NVRAM 130 and DRAM device 140).After the copy is completed, IMC 131 signals RAM disk driver 713 (block740), which in turn signals OS 712 indicating that the I/O is completed.

FIGS. 8A and 8B illustrate a third embodiment of an interface betweensoftware and storage provided by NVRAM 130 with the reference to FIG. 6Baccording to one embodiment of the invention. FIG. 6B illustrates amemory and storage subsystem 682 according to one embodiment of theinvention. In the embodiment shown in FIG. 6B, there is no distinctionbetween mass storage and system memory within NVRAM 130. The OS (OS 850of FIG. 8B) creates a memory-mapped file system, where FM 142 serves asstorage for file system 660. It is understood that NVRAM 130 may includemore or fewer partitions than what is shown in FIG. 6B (e.g., BIOS NVRAM162 and/or TPM NVRAM 172 may be absent).

In a memory-mapped file system, the files used by an application 810(and are, therefore, in a virtual address space 820 allocated toapplication 810) can be directly mapped to NVRAM device address space840. Each address location in NVRAM device address space 840 isdirectly-addressable by the processor, and is, therefore, “resident” inmemory. There is no need to trigger a page fault to bring in a page fromstorage, because OS 850 understands that the storage is the same as thememory. In this embodiment, OS 850 needs modification to utilize NVRAM130 but application 810 can be used without modification. By contrast,in a non-memory-mapped file system, each read/write by an application isa system call. If the read/write is directed to a page not already inthe memory, the access to that page will involve storage I/O accessperformed by a storage driver, which is much slower than memory access.

FIG. 8 B illustrates the embodiment of FIG. 8A with further details.Referring to FIGS. 8A and 8B, when application 810 request a read accessto a page 821 of a file (block 860), OS 850 passes the request to memoryaccess hardware as page 821 is already mapped in memory as page 841(block 870). The memory access hardware (e.g., IMC 131 or a combinationof IMC 131 and NVRAM controller 132) retrieves page 841 from NVRAM 130and forward the page to a cache 830 (e.g., an SRAM or DRAM cache) toreduce future access latency (block 880). The memory access hardwarethen signals OS 850, which in turn signals application 810 that thefetch is completed. Write access to a page can be performed in the sameway as read if the page is not already fetched. Additionally, whenapplication 810 modifies a page 821 that has already been fetched, acopy-on-write can be performed to create a write copy 822 of page 821 invirtual address space 820. This write copy can be stored in cache 830for future access, and can be written back to NVRAM 130 at a later time(e.g., when cache 830 is full and needs to make space for a newlyfetched page).

FIG. 9 an interface between software and storage provided by NVRAM 130according to a fourth embodiment of the invention. This secondembodiment refers to memory and storage subsystem 682 of FIG. 6B, inwhich both the OS and applications (e.g., an application 910) needmodification to utilize NVRAM 130. The concept of storage disappears inthis embodiment. In this embodiment, application 910 can manage NVRAMdevice address space 930 using memory access instructions. For example,application 910 can call a set of OS Application Programming Interface(APIs) 920 to perform equivalents of memory_allocation,memory_deallocation, memory_read, memory_write, etc. Each of theseinstructions can be directed at a particular address location in NVRAM130. Thus, application 910 owns the responsibility of managing thepersistence and optimal write management of the data written to NVRAM130.

The techniques shown in the diagrams of FIGS. 4, 5, 7, 8A, 8B and 9 canbe implemented using instructions and data stored on non-transitorymachine-readable or computer-readable media, such as non-transitorymachine-readable or computer-readable storage media (e.g., magneticdisks; optical disks; random access memory; read-only memory; flashmemory devices; and phase-change memory).

Embodiments of the invention may also be provided as a computer programproduct which may include a non-transitory machine-readable mediumhaving stored thereon instructions which may be used to program acomputer (or other electronic device) to perform a process. Thenon-transitory machine-readable medium may include, but is not limitedto, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks,ROMs, RAMs, EPROMs, EEPROMs, magnet or optical cards, propagation mediaor other type of media/machine-readable medium suitable for storingelectronic instructions. Embodiments of the invention may also bedownloaded as a computer program product, wherein the program may betransferred from a remote computer (e.g., a server) to a requestingcomputer (e.g., a client) by way of data signals embodied in a carrierwave or other propagation medium via a communication link (e.g., a modemor network connection).

While the invention has been described in terms of several embodiments,those skilled in the art will recognize that the invention is notlimited to the embodiments described, can be practiced with modificationand alteration within the spirit and scope of the appended claims. Thedescription is thus to be regarded as illustrative instead of limiting.

What is claimed is:
 1. An apparatus comprising: a processor to executesoftware; memory coupled to the processor, at least a portion of thememory comprising a non-volatile random access memory (NVRAM) that isbyte-rewritable and byte-erasable by the processor; and a memorycontroller coupled to the NVRAM to perform a memory access operation toaccess the NVRAM in response to a request from the software for accessto a mass storage.
 2. The apparatus of claim 1, wherein the NVRAMcomprises phase change memory (PCM).
 3. The apparatus of claim 1,wherein the NVRAM comprises phase change memory and switch (PCMS). 4.The apparatus of claim 1, wherein the NVRAM comprises a partition thatis exposed to the software as the mass storage and the memory controlleremulates the mass storage to a storage driver in response to the requestfrom the software.
 5. The apparatus of claim 1, wherein a portion of theNVRAM is configured as a random access memory (RAM) disk.
 6. Theapparatus of claim 1, wherein the NVRAM stores a file system thatcontains a file, which is mapped to a virtual address space of anapplication executed by the processor, such that access to the fileincurs no page fault.
 7. The apparatus of claim 1, wherein the processorexecutes an application that performs memory operations to allocate andaccess an address space of the NVRAM.
 8. A method comprising: receiving,by a memory controller, a request from software executed by a processorto access a mass storage; and performing, by the memory controller, amemory access operation in response to the request to access anon-volatile random access memory (NVRAM) that is byte-rewritable andbyte-erasable by the processor.
 9. The method of claim 8, wherein theNVRAM comprises phase change memory (PCM).
 10. The method of claim 8,wherein the NVRAM comprises phase change memory and switch (PCMS).
 11. Asystem comprising: a processor to execute software; memory coupled tothe processor, a first portion of the memory comprising a dynamic randomaccess memory (DRAM) and a second portion of the memory comprising anon-volatile random access memory (NVRAM) that is byte-rewritable andbyte-erasable by the processor; and a memory controller coupled to theNVRAM to perform a memory access operation to access the NVRAM inresponse to a request from the software for access to a mass storage.12. The system of claim 11, wherein the NVRAM comprises phase changememory (PCM).
 13. The system of claim 11, wherein the NVRAM comprisesphase change memory and switch (PCMS).
 14. The system of claim 11,wherein the NVRAM comprises a partition that is exposed to the softwareas the mass storage and the memory controller emulates the mass storageto a storage driver in response to the request from the software. 15.The system of claim 11, wherein a portion of the NVRAM is configured asa random access memory (RAM) disk.
 16. The system of claim 11, whereinthe NVRAM stores a file system that contains a file, which is mapped toa virtual address space of an application executed by the processor,such that access to the file incurs no page fault.
 17. The system ofclaim 11, wherein the processor executes an application that performsmemory operations to allocate and access an address space of the NVRAM.